Photoelectric phonograph



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. www? H H May 20, 1941 M. L. THOMPSON ruoToELacTRrc PHouoGRAPH FiledDec. 13, 1940 Patented May 2G, 194i UNT. S

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rnoroaeacrarc rnonoeaern Applica-tien December i3, 1940, Serial No.370,083

l1 Claims.

This invention relates to radio-phonograph combinations employingphotoelectric pickup devices, 'and more particularly to the energizationof the light sources of said photoelectric devices. The improved lightsource energizing means of the present invention may be advantageouslyemployed in connection With photoelectric sound reproducing systems ingeneral, but `is particularly adapted for use with photoelectric pickupsof the type employed in the reproduction of mechanical (e. g. disc)recordings. A photoelectric pickup device of this type is disclosed, forexample, in the -copendng application of E. O. Thompson, Serial No.357,322, filed September 18, 1940.

Photoelectric phonograph pickup devices for use with mechanicalrecordings usually comprise a light source, a mechanical system formodulating or fluctuating the beam of light from said source inaccordance with the recorded sound, and a photoelectric cell which isexposed to the modulated light beam and which, under the influence ofthe light, functions to generate an electrical signal whose waveform isproportional to the fluctuations in said beam of light. Since thephotoelectric cell responds to minute variations in the level ofillumination, it is necessary to employ a light source which provides anillumination substantially free of variations in intensity, particularlyof cyclical variations occurring fat audio frequencies. A simple way ofsecuring such an even illumination is to operate the lamp from a directcurrent source, for example from a battery, or from an alternatingcurrent power pack comprising rectier and lyter means. Neither of theseeXpedients is convenient, however, particularly Where the equipment isto be employed in radio-phonographs intended for home use.

'Ihe principal object of the present invention is to provide novel andconvenient means for energizing the lamp of the photoelectric pickup ina radio-phonograph combination employing such a pickup.

In accordance with this invention-it is proposed to employ theoscillator circuits of the radio receiver as a source of high frequencycurrent for heating the filament of the lamp to incandescence. If theoscillator is adjusted to operate at a super-audible frequency, e. g. atradio frequency, no audible signal can be generated by the photoelectriccell since the variations in illumination provided by the lamp willoccur at a frequency beyond audibility,- specifically at double thefrequency of the current supplied by the oscillator. Moreover, .at highfrequencies, the actual variation in illumination will be extremelysmall .due to the thermal lag of the filament winding as compared to theperiod of the high frequency heatingv curn rent.

Another object of the invention is to provide a novel circuitarrangement whereby the energy available from the oscillator isincreased during the operation of the phonograph.

Other objects and features of the invention will appear hereinafter.

The invention may best be understood by reference to the accompanyingdrawing, the single figure of which is a diagrammatic illustration of aradio-phonograph combination embodying the invention.

, Referring to the drawing, the phonograph- ,to the mirror by means ofthe crank arm 8 causes the mirror to be vibrated about the central axis9 which extends perpendicularly to the plane of the record. The lamp andcell Iare preierably so adjusted with respect to the mirror that thebeam of light is normally half on and half off the cell 4, so that whenthe pickup is placed on a record, the undulations of the reccrd grooveswill cause the illuminated area of the cell to vary in accordance withthe said undulations. rIhe electrical output of the photoelectric cell 4may be applied to a Suitable amplier by way of the lead wires I0, whilethe lamp 2 may be energized from a suitable current source by way of thelead wires I I.

The radio receiving apparatus illustrated in Fig. 1 comprises a radiofrequency amplifier I2, first detector I3, oscillator means comprisingthe vacuum tube V1 and associated tuned circuits, intermediate frequencyamplifier I4, second detector I5, audio frequency amplifier I 5,loudspeaker L. S., and a power supply source I'I. In the specificembodiment shown, a four-position Wave band switch is provided formaking all connections necessary for selective operation of theapparatus as a phonograph, as a radio with push employed to give a bandspread effect. Vshortvrave position of the gang'switch, as well as inthe other two radio positions-the oscillator button` control, or withmanual control in either the broadcast or short wave bands. These positions of the wave band switch are designated by the Band indicatorhaving positions lettered Phono, P. B, B. C., and S. W. respectively.V

In the short wave position (S. W.) of the band switch, the oscillatortube V1 is connected,y by way of the condenser i3 and gang switchsection S1, to the short wave coil I9 and the variable tuning condenser26. rThe condenser 2i is connected in series with the variable condenser23" in this position of the band switch and may be In the signal may besupplied to the first'deteetor stage I3 by way of the lead 22 and thev'gang switch section Sz. Any of the conventional mixing circuits may beemployed.

' In the manual broadcast position'(B. C.) of the band switch,the'oscillator tube is connected to the` broadcast coil 23 and thevariable tuning condenser 2i). The coil 23 may be shunted by a paralleltrimmer condenser as shown, while the series trimmer condenser 23 may beinserted serially in the variable tuning condenser circuit as is wellunderstood in the art.

In the push button position, the coil 23 and its shunt trimmer condenseris retained in the circuit, but any one of the preadjusted individu allyselectable trimmer oondensers 25, 26 or 21 may be substituted for thevariable tuning con-v denser 20.' p In any of the three positions of thewave band switch above referred to, the oscillator tube V1 may besupplied with plate current from the Bv supply Il through a shunt feedsystem comprising the voltage dropping resistor 28, the R. F.

coil 33 to the lamp 2 in the Phono position of the gang switch. Thecoupling between the coils 23 and 33 should be adjusted to ensure anefficient transfer of energy from the oscillator V1 to the lamp 2.Inductive coupling between the coils 23 and 33 is indicated by thesymbol M.

Although, as indicated above, it is possible to utilizeone of thereceiver coils I3 or 23 as a part of the oscillator circuit when thetube V1 is used to supply heating current to the incandescent lamp 2, itwill be understood that where desired a separate `coil may be providedfor exclusive use in connection with the phonograph operation of thesystem. Although heating current frequencies have been found to be notcritical, frequencies of about 1800 kilocycles have been used for thispurpose, since such frequencies are conveniently obtained when shuntingthe regular broadcast band oscillator coil 23 with a small trimmer'condenser 32, as shown.

`Since the power requirement of the lanrp 2 is relatively high ascomparedfto the normal power output of an oscillator' employed in itsusual capacity in adetector-oscillator circuit, it may 'benecessa-ry tosupplyto the oscillator a substantiaily greater than normal platevoltage.

three radio positions of section Se of the band switch, the resistor 28will be inserted serially in the lead from the plate supply source i1 tothe anode of the tube V1. It may further be noted that in theabove-mentioned three radio positions, the output of the second detectori5 is connected to the input of the audio frequency ampliier le, and thecathode or cathodes of the one or more intermediate frequency amplifiertubes V2 are connected to chassis or ground through the gang switchsection S7.

In the phonograph position of the band switch (shown) the oscillatortube remains connected tol the broadcast coil 23, the preadjusted tuningcon-` tankV circuit 23, 32 by means of the coil 3-3 and" thelamp vleadsil. The gang switch section S4, it will be noted, connects theungrounded end of This may be accomplished in theV circuit illustrateclby short circuiting the voltage dropping resistor 23-by means ofthegang' switch section Se. Thus, the oscillator V1 may be suppiied withthe full output voltage of' the B supply Il, since there will be only anegligible direct current vole tage drop in the R. F. choke 29. the Bsupply l1 be not overloaded by the unY usually heavy oscillator load, itmay be desirable to kdecrease the current consumption of those radioreceiver circuits notdirectly involved when the apparatus is employed asa phonograph. This may be effected, for example, by open-circuiting theplate and screenV circuits of the radio and intermediate frequencyamplifiers and of the firstdetect'or. In the illustration, by way ofexample, they intermediate frequency'amplifiery tube V1 is providedwith'the switch S7 in its cathode* circuit. This switch is closed in thethree radio positions' of the lwave 'band switch, but is open in thePhono position' thereof.A This arrangement makes it possible to supplyadequate power to the oscillator tube witho'utr'esorting to power supplysystems having 'greater than normalY power output capacity.

Insome instances it may be found expedient to omit the gangswitch'section S4 entirely, thereby sin'iplifyingA the design fof thegang switch. In this case the connectionV eected by the switch S4 asillustrated in the drawing would be made permanent. Under these"conditions the lamp 2 Vremains a load'on the oscillator tube V1 duringvoltagereductio may be of such an order that,

during radio reception,- thevlamp 2 is so feebly eircitedthat it failsto glow, or just` barely glows;

The switch Sa-may then be regarded as a means for increasing the radiofrequency energy sup-- plied t the lamp 2 duringphoncgraph operation.

oscillator tubeshouldY beY selected which is capable of generatingsumcient high frequency' In order that power to satisfactorily excitethe lamp in the photoelectric pickup head. A type 7B5 pentode which israted at 3.4 Watts when supplied with 250 volts at the plate has beenfound capable of driving a lamp rated at 3.3 volts and 0.6 amperevrepresenting a power consumption of about 2 watts.` Lamps containing anatmosphere of an inert gas, such as argon, for improved filament life,have been found satisfactory for use in photoelectric pickups vof thetype referred to herein. Where the `lamp is mounted in thepickup head,and, therefore, may be subjected to some vibration, it is desirable toselect lamps having filaments designed and mounted in such a manner asto be free from microphonics.

'Ihe electrical output ofthe photoelectric cell maybe applied directlyto the input of the audio frequency amplier I6 by Way of the gang switchsection S5, or, if desired, a preamplifier 34 may be inserted ahead ofthe amplifier I6. pre-amplifier for use with amplitude-responsivephotoelectric pickups, when used in combination with constant velocityrecordings, is fully described in a copending application of M. L.Thompson and E. O. Thompson, Serial No. 361,968, lled October 19, 1940.

The herein-disclosed embodiment of the invention is illustrative of thenovel features thereof, and is not to be taken as limiting theinvention. It will be apparent to those skilled in the art that furtherembodiments and modifications of the invention are possible within thescope of the appended claims.

I claim:

1. In a radio-phonograph combination, a radio receiver of thesuperheterodyne type including a local oscillator, an electro-opticalphonograph pickup device including an electric lamp, switching means forselectively eiecting radio or phonograph operation, and means operableby said switching means for coupling said lamp to said oscillator duringphonograph operation, thereby to supply energy from said oscillator tosaid lamp.

2. In a radio-phonograph combination, a radio receiver circuit of thesuperheterodyne type including a high frequency vacuum tube oscillatorcircuit, a photoelectric phonograph pickup device including a lightsource comprising an electric lamp, means for selectively effectingradio or phonograph operation, and means for supplying energy from saidoscillator circuit to said lamp during phonograph operation.

3. In a radio-phonograph combination, a radio receiver of thesuperheterodyne type including a local oscillator, an electro-opticalphonograph pickup deviceincluding an electric lamp, a multipositionswitch, means including contacts on said switch for selectivelyeffecting radio r phonograph operation, and means including additionalcontacts on said switch for coupling said lamp to said oscillator duringphonograph operation, thereby to supply energy from said oscillator tosaid lamp.

4. In a radio-phonograph combination, a radio receiver of thesuperheterodyne type including a local oscillator having a tank circuit,an electrooptical phonograph pickup device including an electric lamp,an energy supply circuit for said lamp coupled to said tank circuit,switching means for selectively effecting radio or phonograph operation,and means controlled by said switching means for rendering said supplycircuit operative only during phonograph operation, thereby to supplyenergy from said oscillator to said lamp.

A suitable 5. In a radio-phonograph combination, a multi-band radioreceiver. of the superheterodyne type including a local oscillator, anelectro-optical phonograph pickup device including an electric lamp, amulti-position switch 4for operating said receiver in diierent frequencybands and for selectively eiecting radio or phonographV operation, andmeans including contactsonsaid switch for coupling said lamp to saidoscillator during phonograph operation, thereby to supply energy fromsaid oscillator to said lamp.

6. In a radio-phonograph combination,` a multi-band radio receivercircuit of the superheterodyne type, a multi-band vacuum tube oscillatorcircuit for said receiver, said oscillator circuit comprising aplurality of tunable tank circuits capable of being tuned over aplurality of wavebands, switching means for selectively effecting radioor phonograph operation and for selecting any one of said tank circuitsto enable said radio receiver to be tuned over a desired one of saidwave-bands, a photoelectric phonograph pickup device including a lightsource comp-rising an electric lamp, and means for operating saidoscillator circuit at a frequency whose second harmonic is beyond therange of audibility and for supplying energy from the oscillator circuitto said lamp during phonograph operation.

7. In a radio-phonograph combination, a radio receiver circuit of thesuperheterodyne type including a high frequency vacuum tube oscillatorcircuit, a photoelectric phonograph pickup device including a lightsource comprising an electric lamp, means for selectively eiecting radioor phonograph operation, means for supplying energy from said oscillatorcircuit to said lamp during phonograph operation, and means forsupplying greater-than-normal anode voltage to said oscillator tube whenthe oscillator circuit is utilized to excite said lamp during phonographoperation.

8. In a radio-phonograph combination, a radio receiver circuit ofthe-superheterodyne type including vacuum tube amplifiers and a highfrequency vacuum tube oscillator circuit, a source of limited energysupply for said vacuum tube oscillator and for the vacuum tubeamplifiers in said receiver circuit, a photoelectric phonograph pickupdevice including a light source consisting of an electric lamp, meansfor selectively electing radio or phonograph operation, means forsupplying energy from said oscillator circuit to said lamp duringphonograph operation, and

means for opening the space current circuits of one or more of thosevacuum tubes which function solely in the radio circuits, duringphonograph operation, thereby to increase the amount of energy availableto said oscillator tube from said supply source when said tube isutilized to excite said lamp.

9. In a radio-phonograph combination, a radio receiver circuit of thesuperheterodyne type including vacuum tube amplifiers and a highfrequency vacuum tube oscillator circuit, a source of limited energysupply for said vacuum tube oscillator and for the vacuum tubeamplifiers in said receiver circuit, a photoelectric phonograph pickupdevice including a light source consisting of an electric lamp, meansfor selectively affecting radio or phonograph operation, means forsupplying energy from said oscillator circuit to said lamp duringphonograph operation, and means operative during phonograph operation toreduce the number of individual vacuum tube loads on said energy supplysource and for incr'easingthe voltage on'sai'd oscillator tube,

Vthereby to increase the high'frequency power availableffor theexcitation of said*Ianniy Y 10. In a combined carrierWaVeLreeiVer-phonograph combination, carrierWavereceiving'apparatus'including high frequency current generatingmeans forming an Voperative part ofjsaid apparatus, an Yeleotro-opticalphonograph pickup device including anelectric lamp, means forselectively effectingV carrierwiraA/eVV reception or phonographoperation, and means for supplying high frequency current' from saidgenerating means to said Alamp during phonograph operation.

11. In a radio-phonograph combination, a

MILTON L. THOMPSON.

